1. Field of the Invention
The present invention relates to a charged particle beam apparatus, an abnormality detecting method for a digital-analog (DA) converter unit, a charged particle beam writing method, and a mask. For example, the present invention related to an electron beam writing method and apparatus which deflect a variably shaped electron beam to irradiate the electron beam on a target object. Furthermore, the present invention relates to an abnormality detecting method for a digital-analog converter (DAC) amplification unit (to be simply referred to as DAC amplifier) to deflect an electron beam.
2. Related Art
A lithography technique which leads development of micro-patterning of a semiconductor device is a very important and only one process which generates a pattern in semiconductor manufacturing processes. In recent years, with high integration of an LSI, a circuit line width required for semiconductor devices progressively decreases year by year. In order to form a desired circuit pattern on the semiconductor devices, a high-precision master pattern plate (also called a reticle or a mask) is necessary. An electron beam writing technique has an excellent resolution and is used in production of a high-precision master pattern plate or a mask.
FIG. 11 is a conceptual diagram for explaining an operation of a variable-shaped electron beam photolithography apparatus. A variable-shaped electron beam photolithography apparatus (EB (Electron Beam) writing apparatus) operates as follows. In a first aperture plate 410, rectangular opening 411, a square, for example, is formed to shape an electron beam 330. In a second aperture plate 420, a variable-shaping opening 421 is formed to shape the electron beam 330 having passed through the opening 411 to a desired variable rectangular shape. The electron beam 330 irradiated from a charged particle source 430 and having passed through the opening 411 of the first aperture plate 410 is deflected by a deflector. The electron beam 330 passes through a part of the variable-shaping opening 421 and is irradiated on a target object 340 placed on a stage. The electron beam 303 having passed through the variable-shaping opening 421 is deflected by a deflector and irradiates at a predetermined position of the target object 340. Irradiations of the electron beams shaped by the opening 411 and the variable-shaping opening 421 on the predetermined position on the target object 340 are combined to each other to make it possible to write an arbitrary pattern at a high-speed. Since a range in positioning beams by deflection is limited, the target object is placed on an X-Y stage, and writing of a predetermined pattern in a large area can be performed by moving the stage. A scheme which continuously moves the stage in a predetermined direction (for example, an X direction) during writing to improve the writing time may be employed. A scheme which causes an electron beam to pass through both the opening 411 and the variable-shaping opening 421 to form an electron beam having a variable shape is called a variable shaping scheme.
As described above, in a writing apparatus, a charged particle beam such as an electron beam is deflected to write a pattern. In this beam deflection, a DAC amplifier unit (to be simply referred to a DAC amplifier) is used. As roles of the beam deflection using the DAC amplifier unit, for example, control of the shape and size of a beam shot, control of the position of a beam shot, and blanking of a beam are known.
In this case, when an error occurs in the DAC amplifier unit, an amount of beam deflection is different from a desired deflection amount. For this reason, abnormal or defective writing consequently occurs. However, abnormal writing caused by an error in the DAC amplifier unit is often detected by an inspection of a written pattern. This is because abnormality of the DAC amplifier unit cannot be detected during writing. For this reason, writing is continuously done with the abnormal DAC amplifier unit, the writing continues in an abnormal writing state. As a result, the defective masks are continuously written to make heavy losses in mask manufacturing.
A technique which measures settling times of the DAC amplifier units at high accuracy by measuring a change in voltage at a middle point of a measuring resistor connected between outputs of two DAC amplifier units, while a deflection data is input to one of the DAC amplifiers, and the opposite deflection data is input to the other DAC amplifier with a delay time, is disclosed in a reference (for example, see Published Unexamined Japanese Patent Application No. 2004-259812 (JP-A-2004-259812)), though this is not related to the detection of abnormality of the DAC amplifiers.
As described above, since abnormal or defective writing occurs when an error occurs in the DAC amplifier unit, a method of detecting abnormality of the DAC amplifier unit is demanded. Furthermore, the abnormality of the DAC amplifier unit includes the following cases. That is, the DAC amplifier unit may be completely broken, and the DAC amplifier may be abnormal only under a specific condition. Furthermore, when abnormality occurs under a specific condition, the abnormality may be repeatable or may not be repeatable. In particular, when repeatability is not maintained, the abnormality of the DAC amplifier unit cannot be easily identified, and a long time is required until the problem is resolved. And, when the level of abnormality of the DAC amplifier unit is small, an amount of abnormality of a written pattern is also small. For this reason, the abnormality may not be detected in pattern inspection after writing. In this case, abnormal or defective masks, abnormal or defective wafers, and the like are continuously written (manufactured), and secondary damage in manufacturing may occur. Therefore, a technique and device for detecting an abnormal/erroneous operation of a DAC amplifier unit at high accuracy on real time during writing a pattern is very useful. Abnormality detection for a DAC amplifier unit (or simply called DAC amplifier) serving as an example of a DA converter is necessary for not only a writing apparatus but also all apparatuses having a function that deflects a charged particle beam by using a DA converter unit.